Parents attempt to use a strong disciplinary approach with their teens, often with frustrating results. This "old school" approach doesn't work with older teens because they want freedom more than anything else. It is their top value (along with friends and a focus on themselves).
Family systems can be closed or open. In a closed system, teens are given orders, threats, and warnings by their parents. In a totally open family, teens are allowed to do what they want, and parents often throw up their hands when the going gets tough. The first approach puts teens on a short leash, while the second puts them on one that is too long.
The ideal system is somewhere in between. Teens need enough direction and control to guide them, yet enough room to let them breathe, learn, and discover. There must to be a balance between structure and flexibility.
To sum up, a strong disciplinary approach overlooks the need for growth and exploration during the teen years, especially those who have just graduated from high school. So, let out the leash some, and watch what happens. You might even enjoy it too.